Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session M54: Emergent Properties of Complex Oxides Bulk, Thin Films, and Heterostructures IIIFocus
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Sponsoring Units: GMAG Chair: Anand Battacharya, Argonne National Laboratory Room: Room 306 |
Wednesday, March 8, 2023 8:00AM - 8:36AM |
M54.00001: Spin-Heat Coupling and Thermal Spin Transport in Rare-Earth Iron Garnet Heterostructures Invited Speaker: Hariharan Srikanth Spin-heat coupling and thermal spin transport are topical areas of interest in magnetism. The origin of Spin Seebeck effect (SSE) and its relationship with magnetic anisotropy as well as magnon propagation across magnetic insulator/heavy metal interfaces have remained challenging issues. We have pioneered the technique of RF transverse susceptibility to probe the effective magnetic anisotropy in magnetic materials and heterostructures. Combining these experiments with SSE and anomalous Nernst effect (ANE) measurements, we have shown correlation between bulk and surface anisotropy with the field and temperature dependence of SSE in yttrium iron garnet (YIG)/Pt heterostructures and other compensated ferrimagnets [1,2]. Recently, our group has shown, for the first time, a scaling of longitudinal SSE in gadolinium iron garnet (GdIG) films with different thickness and on different substrates across the compensation temperature [3]. Our ongoing work on thulium iron garnet (TmIG) heterostructures with varying film thickness reveals the clear role of anisotropy and damping on the SSE. From RF susceptibility, SSE and FMR spin pumping experiments, quantitative analysis of the magnon propagation length has been done. Overall, this talk would present new results in the thermal spin transport of garnet heterostructures which are of fundamental importance in spintronics. |
Wednesday, March 8, 2023 8:36AM - 8:48AM |
M54.00002: Magnetic fluctuations in an XY quantum magnet CoTiO3 Jeongheon Choe, Andrey Baydin, David Lujan, Gaihua Ye, Martin A Rodriguez-vega, Fuyang Tay, Jiaming He, Jianshi Zhou, Gregory A Fiete, Junichiro Kono, Rui He, Xiaoqin Elaine Li Cobalt titanate, CoTiO3 is an easy-plane quantum antiferromagnet with bond-dependent exchange couplings and it has been shown to host topological magnon modes [1, 2]. Magnetic excitations are characterized by fluctuations of phase and amplitude of the magnetic order parameter. Here we report zone center magnon modes that are detectable in both Raman and THz absorption experiments and how transverse and longitudinal magnetic fluctuations associated with these modes are manifested. We quantify the coupling between longitudinal fluctuations and transverse magnons, via analysis of asymmetric spectral line shape. |
Wednesday, March 8, 2023 8:48AM - 9:00AM |
M54.00003: Studying the effect of boron doping and temperature on antiferromagnetic domains in epitaxial Cr2O3 films using diamond magnetometry Abdelghani Laraoui, Adam D Erickson, Ather Mahmood, Syed Qamar Abbas Shah, Ilja Fescenko, Rupak Timalsina, Christian Binek The antiferromagnetic (AFM) magnetoelectric chromia (Cr2O3) is an archetypical oxide that permits voltage-control of the Néel vector in the presence of an applied magnetic field, but it suffers practical limitations due to its low Néel Temperature (TN) ~ 307 K [1]. Boron doping increases TN to 400 K and allows realizing voltage controlled Néel vector at zero magnetic field [2], a promising result for AFM spintronics. To date there is no direct measurement of TN in B-Cr2O3, and it is not clear how doping affects its AFM properties. Here we use nitrogen vacancy (NV)-magnetometry [3, 4] to directly study the effect of B doping and temperature on the properties of AFM domains in 200-nm thick Cr2O3 and B-Cr2O3 films grown by pulsed laser deposition on AL2O3 substrates. Magnetic contrast, domain size, domain width, and TN are compared for different temperatures, growth and interfacial conditions. By using reverse propagation protocol [3,4], we measure the magnetization profile, which shows well-defined magnetized nano-domains, affected strongly by temperature and B doping. [1] N. Wu et al., Phys. Rev. Lett. 106, 087202 (2011). [2] A. Mahmood et al. Nat. Comm. 12, 1674 (2021). [3] P. Appel et al., Nano Lett. 19, 1682 (2019). [4] A. Erickson et al., RSC Advances, Under review (2022). |
Wednesday, March 8, 2023 9:00AM - 9:12AM |
M54.00004: Creation and control of dynamical ferroelectric skyrmions via orbital angular momentum of light Lingyuan Gao, Sergei Prokhorenko, Yousra Nahas, Laurent Bellaiche Using first-principle-based effective Hamiltonian simulations, we show that the optical vortex beam can excite and drive dynamical electrical skyrmions in ferroelectric thin films. More specifically, skyrmions are created and annihilated alternately at the two interfaces, and experience a periodic transition from a markedly “Bloch” character to a “Néel” character with rotation of dipole components. The mechanism is very robust in the sense that skyrmions are well maintained under different conditions and are highly tunable by controlling external variables. Our study thus demonstrates that this unique light-matter interaction can be very powerful in creating and manipulating topological solitons in functional materials. |
Wednesday, March 8, 2023 9:12AM - 9:24AM |
M54.00005: Revealing Emergent Magnetic Charge in a Topological Antiferromagnet with Diamond Quantum Magnetometry Hariom Jani, Anthony Tan, Michael Hoegen, Lucio Stefan, Claudio Castelnovo, Daniel Braund, Alexandra Geim, Matthew Feuer, Helena S Knowles, Ariando Ariando, Paolo G Radaelli, Mete Atatüre Whirling topological textures play a key role in exotic phases of magnetic materials and offer promise for logic and memory applications. In antiferromagnets, these textures exhibit enhanced stability and faster dynamics with respect to ferromagnetic counterparts, but they are also difficult to observe due to their vanishing net magnetic moment. Diamond quantum magnetometry offers a promising route to image such weak features through its high sensitivity and vectorial field detection. Here, we image the topological textures in the archetypal antiferromagnet, hematite, and reveal that these textures host in parallel a rich tapestry of monopolar, dipolar and quadrupolar magnetic charge distributions. By extracting field orientations, we demonstrate direct readout of the previously inaccessible antiferromagnetic vorticity, which is connected to magnetic charge through a duality relation. Our work highlights the critical role that diamond quantum magnetometry could play in exploring emergent phenomena and topological spintronics in quantum materials. |
Wednesday, March 8, 2023 9:24AM - 9:36AM |
M54.00006: Emergent Magnetism at the AlOx/KTaO3 Interface Probed with mK Transport Measurements Patrick W Krantz, Alexander C Tyner, Pallab Goswami, Venkat Chandrasekhar Here we report signatures of emergent magnetism measured through electrical transport on the two-dimensional electron gas (2DEG) hosted at the interface between AlOx and KTaO3 (KTO). In samples fabricated to suppress superconductivity we see a gate voltage tuned magnetism characterized by a zero-field transverse voltage that is strongly asymmetric with respect to an applied perpendicular magnetic field and becomes strongly hysteretic at the lowest measured temperatures. These results are discussed for three different crystal terminations of KTO, and interpreted based on the complex spin texture of the KTO surface. Density functional theory results confirm that oxygen vacancies result in a net spin polarization leading to a finite Berry curvature, explaining the transverse voltage and the striking hysteretic behavior. We also discuss compelling related results measured at higher temperatures in non-local differential resistance. |
Wednesday, March 8, 2023 9:36AM - 9:48AM |
M54.00007: Effects of Boron surface accumulation on the Néel temperature revealed in B-doped Cr2O3 films Ather Mahmood, Jamie L Weaver, Syed Qamar Abbas Shah, Will Echtenkamp, Jeffrey W Lynn, Christian Binek Multi-functional thin films of boron (B) doped Cr2O3 grown by pulsed laser deposition exhibit voltage-controlled and nonvolatile Néel vector reorientation in the absence of a magnetic field. Isothermal toggling of antiferromagnetic states is demonstrated in prototype device structures at CMOS compatible temperatures between 300 K and 400 K. A strict determination of TN is essential but has remained elusive most likely due to a thermally activated runaway effect of the Néel temperature. This behavior can be understood by considering the B-enrichment due to the phenomenon of surface segregation. Cold Neutron Depth Profiling (cNDP), performed at National Institute of Standards and Technology, points at progressing depletion of B in the bulk and B-accumulation near the surface. By using X-ray Photon Spectroscopy and Spin Hall measurements, we demonstrate a shift in TN towards higher values of ≈ 477 K, associated with the increase in B-concentration within an interfacial layer of about 70 nm. |
Wednesday, March 8, 2023 9:48AM - 10:00AM |
M54.00008: Experimental evidence of t2g electron-gas Rashba interaction induced by asymmetric orbital hybridization Ganesh Ji Omar, Ariando Ariando, Hariom Jani, Weilong Kong, Zhi Shiuh Lim, Saurav Prakash, Sonu Hooda, Thirumalai V Venkatesan, Yuan P Feng, Stephen J Pennycook, LEI SHEN We report the control of Rashba spin-orbit interaction by tuning asymmetric hybridization between Ti-orbitals at the LaAlO3/SrTiO3 interface. This asymmetric orbital hybridization is modulated by introducing a LaFeO3 layer between LaAlO3 and SrTiO3, which alters the Ti-O lattice polarization and traps interfacial charge carriers, resulting in a large Rashba spin-orbit effect at the interface in the absence of an external bias. This observation is verified through high-resolution electron microscopy, magneto-transport and first-principles calculations. Our results open hitherto unexplored avenues of controlling Rashba interaction to design next-generation spin-orbitronics. |
Wednesday, March 8, 2023 10:00AM - 10:12AM Author not Attending |
M54.00009: Structural, compositional and magnetic study of the transformation of a hematite thin film into a magnetite/hematite epitaxial bilayer Oscar Rodriguez, Mauricio Prieto, Lucas Caldas, Liviu C Tanase, Eugenia Sebastiani, Jesús López-Sánchez, Thomas Schmidt, Juan Rubio-Zuazo Oxides, as a wide class of materials with a huge range of functionalities, give rise to novel phenomena when different types are combined in heterostructures, whose production is an everlasting topic in the development of new materials. Thus the exploration of new fabrication methods is mandatory. Low energy ion bombardment has been used on single-crystalline oxide thin films to produce epitaxial layers of the corresponding suboxides [1,2]. We have carried out an investigation of the magnetite/hematite epitaxial bilayer (Fe3O4(111)/α-Fe2O3(0001)) on different substrates, which is an ideal oxide system to study magnetic exchange effects at the interface. The characterization of both systems has included structural, chemical and magnetic properties. We have used synchrotron-based experimental techniques such as Surface X-ray Diffraction (SXRD), Hard X-ray Photoemission Spectroscopy (HAXPES), Low Energy Electron Microscopy (LEEM), Photoemission Electron Microscopy (PEEM) or X-ray Circular Magnetic Dichroism (XCMD). The aim of this work has been to obtain microscopic information on the as-grown material and on the evolution of the materials during the ion bombardment, as well as during high temperature annealing of the bilayers. Ion bombardment gradually reduces the initial hematite into a defective sub-oxide where magnetite nuclei start to grow with increasing ion doses and coalesce into a defective epitaxial magnetite upper layer. Two rotational domains emerge, with small grains which are typically a few tens of nanometres large. They do not grow significantly with temperature annealings. This robustness may be explained by the incoherent growth of the grains which may favour the formation of twin or antiphase boundaries. The distribution of magnetic domains, as visualized with XCMD, shows no apparent correlation with the structural domains. The epitaxial magnetite/hematite bilayer shows a strong exchange bias. However, a very different interfacial exchange interaction appears when Ni film is directly grown on the hematite thin film, which is explained in terms of the interaction between an antiferromagnetic (hematite) and a ferromagnetic (Ni). |
Wednesday, March 8, 2023 10:12AM - 10:24AM |
M54.00010: Engineering Easy-plane Anisotropy in Ferrimagnetic Rare-earth Iron Garnet Yixuan Song, Geoffrey S Beach, Caroline A Ross Rare-earth iron garnets, a ferrimagnetic insulator, have received attention for their many properties including small damping and tunable magnetization and angular momentum compensation temperatures. Most research efforts have been focused on garnet thin films grown on the (111) plane because of their perpendicular magnetic anisotropy (PMA), and the in-plane anisotropy, however neglected, can be important for our understanding of the switching behavior and the energetics of magnetic textures. In-plane anisotropy can be conveniently explored in garnet thin films on (110) planes. Here we combine a theoretical and experimental analysis of the anisotropy landscape for Europium iron garnet (EuIG) epitaxially grown on (110) Gadolinium Gallium garnet (GGG) using pulsed laser deposition. |
Wednesday, March 8, 2023 10:24AM - 10:36AM |
M54.00011: Observation of Topological Hall Effect and Magnetic Textures in Ferrimagnetic (110) NiCo2O4 Films Kun Wang, Qiuchen Wu, Xuegang Chen, Xia Hong We report the observation of topological Hall effect (THE) and magnetic textures in 16 nm (110) NiCo2O4 (NCO) films. Epitaxial NCO films are deposited on (110) MgAl2O4 (MAO) substrates via off-axis RF magnetron sputtering. The films are ferrimagnetic with Curie temperature TC above 370 K and possess in-plane magnetic anisotropy. The saturation magnetization is about 2.2 μB/formula unit. We observe anomalous Hall effect (AHE) in out-of-plane magnetic field H, which exhibits negligible hysteresis and saturates at the high magnetic fields. Below 100 K, prominent THE signal occurs within a narrow magnetic field range close to where AHE saturates. At 4 K, magnetic force microscopy (MFM) imaging shows magnetic bubble domains with an average size of 150 nm emerge at H = 3.0-3.7 kOe, which correlates well with the magnetic field range for the THE. The gradient of the bubble domain suggests the existence of magnetic textures. We also compare the THE and MFM data with the magnetization hysteresis (M-H) curves. Our results suggest the emergence of spin bimerons/merons as the spins rotate from in-plane to out-of-plane orientations in (110) NCO film. |
Wednesday, March 8, 2023 10:36AM - 10:48AM |
M54.00012: Canted spins in orthoferrites RFeO3 Jianshi Zhou The spin-spin exchange interaction as described by the Heisenberg Hamiltonian gives rise to the colinear spin structure. By incorporating the spin-orbit interaction into the Anderson’s theory of superexchange interaction, Moriya derived a new term in the Heisenberg Hamiltonian, the antisymmetric exchange interaction which leads to canted spin structures. The Moriya’s theory provides the microscopic description for the phenomenological theory about the weak ferromagnetism in some antiferromagnetic insulators by Dzyaloshinsky. The Dzyaloshinsky-Moriya interaction (DMI) has been widely applied to account for canted spin structures in a broader range of magnetic materials. In this talk, we will elaborate the weak ferromagnetism in the orthoferrites RFeO3. The canted moment along the c axis in the orthorhombic perovskites with the Pbnm space group was measured by the magnetization in the single crystal samples. The systematic change of the canted moment in the family will be discussed in connection with the structural evolution from LaFeO3 to LuFeO3. The study indicates that the magnetocrystalline anisotropy is responsible for the canted spins instead of the DMI in the orthoferrites. |
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